The prevention of unplanned pregnancy in humans and other mammals is of continuing concern for both the developing and the developed world. A variety of methods and products have been proposed or developed for the prevention of pregnancy. These products include: surgical sterilization, condoms, birth control pills containing progestin or a combination of progestin and estrogen, subdermal implants containing delayed release forms of progesterone, intrauterine devices, spermicidal creams or gels, and intravaginal barriers such as sponges or diaphragms.
Male contraceptive approaches have included the barrier methods, hormonal methods, the rhythm method, and immunological methods. More recently, researchers have begun investigating compounds which inhibit spermatogenesis by disrupting junctional complex sites between Sertoli cells and germ cells in the testes. One such compound is lonidamine (1-(2,4-dichlorobenzyl)-1H-indazole-3-carboxylic acid). Lonidamine belongs to a group of indazole-carboxylic acid compounds that was found to be a potent inhibitor of spermatogenesis. However, the antispermatogenic effects of lonidamine at high doses were found to be irreversible and toxic. See generally Lonidamine: A New Pharmacological Approach to the Study and Control of Spermatogenesis and Tumors, Chemotherapy, 27 Suppl. 2, 1-120 (1981a 1981b); Lonidamine, Proceedings of the 2nd International Symposium, Vancouver (1982).
Several analogues of lonidamine have recently been investigated as spermatogenic inhibitors. See Silvestrini et al., U.S. Pat. No. 6,001,865; Baiocchi et al., U.S. Pat. No. 5,112,986; Silvestrini, U.S. Pat. No. 4,282,237; Palazzo et al., U.S. Pat. No. 3,895,026; Cheng et al., Two New Male Contraceptives Exert Their Effects by Depleting Germ Cells Prematurely from the Testis, BIOLOGY OF REPRODUCTION 65, 449-461 (2001); Grima et al., Reversible Inhibition of Spermatogenesis in Rats Using a New Male Contraceptive 1-(2,4-dichlorobenzyl)-indazole-3-carbohydrazide, BIOLOGY OF REPRODUCTION 64, 1500-1508 (2001); Corsi et al., 1-Halobenzyl-1H-indazole-3-carboxylic acids: A New Class of Antispermatogenic Agents, J. MED. CHEM., Vol. 19, No. 6, 778-783 (1976); Palazzo et al., Synthesis and pharmacological properties of 1-substituted 3-dimethylaminoalkoxy-1H-indazoles, J. MED. CHEM. Vol. 9, 38-41 (1966). Despite these advances, there remains a need for compounds which are antispermatogenic but preferably do not exhibit toxic side effects.
The somatic form of eEF-1 alpha (eEF-1 alpha S) mRNA is virtually undetectable in male and female germ cells of the adult gonad but is very abundant in embryonic cells after the neurula stage. In contrast, another form of eEF-1 alpha (eEF-1 alpha O) mRNA is highly concentrated in oogonia and in previtellogenic oocytes but is undetectable in eggs and embryos. eEF-1 alpha O mRNA is also present in spermatogonia and spermatocytes of adult testis. The latter finding identifies eEF-1 alpha O mRNA as a germ cell-specific gene product. Although germ cells contain very little eEF-1 alpha S mRNA, several eEF-1 alpha S retropseudogenes exist in X. laevis chromosomes. These genes are thought to arise in germ cells from reverse transcription of mRNA and subsequent integration of the cDNA copies into chromosomal DNA. It is suggested that eEF-1 alpha S pseudogenes are generated in primordial germ cells of the embryo before they differentiate into oogonia or spermatogonia. See Abdallah et al., Germ cell-specific expression of a gene encoding eukaryotic translation elongation factor 1 alpha (eEF-1 alpha) and generation of eEF-1 alpha retropseudogenes in Xenopus laevis, Proc. Natl. Acad. Sci. U.S.A. 88: 9277-9281 (1991).
Protein synthesis is believed to be under control of the cell cycle during meiosis and mitosis. Any relationship between substrates for cdc2 kinase and components of the protein synthetic apparatus would therefore be of prime importance. During meiosis of Xenopus laevis oocytes one of the substrates for this kinase is a p47 protein, which is complexed to two other proteins, P36 and P30. Judged from partial amino acid sequence data on P47 and P30, the P30 and P47 proteins were reported to resemble the protein synthetic elongation factors (EF) 1 beta and 1 gamma from Artemia salina. See Belle et al., A purified complex from Xenopus oocytes contains a p47 protein, an in vivo substrate of MPF, and a p30 protein respectively homologous to elongation factors EF-1 gamma and EF-1 beta. FEBS Lett. 255: 101-104 (1989). This paper shows that the complex composed of P30, P47, and P36 from Xenopus is identical to the complex of EF-1 beta, EF-1 gamma, and EF-1 delta from Artemia according to two criteria. 1) Both stimulate elongation factor 1 alpha-mediated transfer RNA binding to ribosomes and exchange of guanine nucleotides on elongation factor 1 alpha to a comparable degree. 2) Each of the three subunits of the protein complex P30.P47.P36 from Xenopus shows a structural homology with one of the corresponding subunits of EF-1 beta gamma delta from Artemia. Presumably the phosphorylation of EF-1 gamma, which associates with tubulin at least in vitro, is important in processes following the onset of meiosis which is accompanied by a rise of protein synthesis. See Janssen et al., A major substrate of maturation promoting factor identified as elongation factor 1 beta gamma delta in Xenopus laevis. J. Biol. Chem. 266: 14885-14888 (1991).